background

background /n.,adj.,vt./ To do a task `in background' is to
do it whenever foreground matters are not claiming your
undivided attention, and `to background' something means to
relegate it to a lower priority. "For now, we'll just print a
list of nodes and links; I'm working on the graph-printing problem
in background." Note that this implies ongoing activity but at a
reduced level or in spare time, in contrast to mainstream `back
burner' (which connotes benign neglect until some future resumption
of activity). Some people prefer to use the term for processing
that they have queued up for their unconscious minds (a tack that
one can often fruitfully take upon encountering an obstacle in
creative work). Compare amp off, slopsucker.

Technically, a task running in background is detached from the
terminal where it was started (and often running at a lower
priority); oppose foreground. Nowadays this term is primarily
associated with Unix, but it appears to have been first used
in this sense on OS/360.